Corrosion resistant material

ABSTRACT

A material which is suitable for equipment in oilfield technology and a process for making the material. The material consist essentially of C, Si, Mn, Cr, Mo, Ni, Cu, N in certain weight percentages, with the balance iron and contaminants due to manufacture. The material is hot formed in a condition free of nitride precipitates and without precipitated associated phases. After a cooling, it is cold formed in a condition free of ferrites. The material has certain values of relative magnetic permeability, yield strength (Rp0.2), notched impact strength, fatigue strength under reversed stresses, and fracture appearance transition temperature.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a National Stage Application of InternationalApplication No. PCT/AT01/00188, filed Jun. 8, 2001 which was publishedunder PCT Article 21(2) in German. Further, the present applicationclaims priority under 35 U.S.C. § 119 of Austrian Patent Application No.A 1133/00 filed on Jun. 30, 2000. Both of these applications areincorporated herein by reference in their entireties.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a material with a high corrosion resistance inmedia with a high chloride concentration, suitable for equipment inoilfield technology, in particular for drilling line components,comprising the elements carbon (C), silicon (Si), manganese (Mn),chromium (Cr), molybdenum (Mo), nickel (Ni), copper (Cu), nitrogen (N),iron (Fe) and contaminants due to manufacture, which material is hotformed and, after cooling, is cold formed.

2. Discussion of Background Information

Corrosion resistant materials which show paramagnetic behavior andfeature a high degree of strength, can be used for equipment in oilfield technology, particularly for drilling line components. However,higher demands are always being made on the parts and stricter standardsare always being set for the materials.

In order to be able to conduct directional measurements during thesinking or boring of a drill-hole with the necessary precision, thematerial must have a permeability of less than 1.005.

A high mechanical strength, in particular a high 0.2% elongation value,is necessary in view of an advantageous design in terms of industrialengineering and of high operational safety of the parts, because it isintended to stress same up to the limiting values of the respectivematerial load capacity, and because increasingly large drilling depthsare required. Furthermore, a notched impact strength of the material isimportant, because the parts often have to withstand high stresses inthe form of impacts or shocks.

A high fatigue strength under reversed stresses is important in manycases, in particular for drilling line parts and drill stems, becauseincreasing or changing stresses can be present during a rotation of theparts or of the drill stems, respectively.

The parts are often installed or used at low temperatures so that thefracture appearance transition temperature (FATT) of the material alsoplays an important role.

The corrosion behavior for parts used in oilfield technology is ofcrucial importance, that is, on the one hand stress corrosion cracking(SCC) and on the other pitting corrosion (pitting, CPT).

As shown by the above statements, materials which have a high degree ofcorrosion resistance in media with a high chloride concentration and aresuitable for equipment in oilfield technology are simultaneously exposedto a plurality of high stresses.

SUMMARY OF THE INVENTION

The object of the invention is to provide a paramagnetic material with ahigh yield strength, high notched impact strength and high fatiguestrength under reversed stresses as well as a low fracture appearancetransition temperature, which at the same time is corrosion-resistant,in particular resistant to pitting, in chloride-containing media.

This object is attained with a material of the type mentioned at theoutset by this consisting essentially of the elements in percent byweight

Carbon (C) less than/equal to 0.03 Silicon (Si) less than/equal to 0.89Manganese (Mn) 0.51 to 4.49 Chromium (Cr) 25.1 to 38.9 Molybdenum (Mo)2.1 to 5.9 Nickel (Ni) 22.9 to 38.9 Copper (Cu) 0.51 to 1.49 Nitrogen(N) 0.17 to 0.29 Iron (Fe) balance

and contaminants due to manufacture, which material is hot formed in acondition free of nitride precipitates and without precipitatedassociated phases and, after a cooling, cold formed in a condition freeof ferrites, and having

a permeability of less than 1.0048

a yield strength (R_(p0 2)) of more than 710 N/mm²

a notched impact strength of over 60 J

a fatigue strength under reversed stresses of more than ±310 N/mm²

at N=10⁷ load reversal and

a fracture appearance transition temperature of less than −28° C.(FATT).

Accordingly, the present invention provides a material which is suitablefor equipment in oilfield technology. This material consists essentiallyof the following elements, in percent by weight, ≦0.03 C; ≦0.89 Si; 0.51to 4.49 Mn; 25.1 to 38.9 Cr; 2.1 to 5.9 Mo; 22.9 to 38.9 Ni; 0.51 to1.49 Cu; and 0.17 to 0.29 N, with the balance iron and contaminants dueto manufacture. The material is hot formed in a condition free ofnitride precipitates and without precipitated associated phases.Moreover, after a cooling, the material is cold formed in a conditionfree of ferrites. The material has a relative magnetic permeability ofless than 1.0048 μr, a yield strength (R_(p0.2)) of higher than 710N/mm², a notched impact strength of higher than 60 J, a fatigue strengthunder reversed stresses of at least ±310 N/mm² at N=10⁷ load reversal,and a fracture appearance transition temperature (FATT) of below −28° C.

In one aspect, the material contains any of the elements in thefollowing weight percentages: C≦0.02, e.g., 0.01 to 0.02; Si≦0.75, e.g.,0.20 to 0.70; Mn 1.1 to 2.9, e.g., 2.01 to 2.6; Cr 26.1 to 27.9, e.g.,26.5 to 27.5 ;Mo 2.9 to 5.9, e.g., 3.2 to 3.8; Ni 27.9 to 32.5, e.g.,30.9 to 32.1; Cu 0.98 to 1.45, e.g., 1.0 to 1.4; and N 0.175 to 0.29,e.g., 0.18 to 0.22.

In another aspect, the material is hot formed at least 3.6-fold and/orcold formed with a degree of forming of less than 38%, e.g., 6 to 19%.In the case of cold forming, the forming temperature may be from 100 to590° C., e.g., from 360 to 490° C. For example, the material may be hotformed at least 3.6-fold and cold formed with a degree of forming of 6to 19% at a temperature ranging from 360 to 490° C.

In another aspect, the material has a pitting potential in a neutralsolution at room temperature of more than 1,100 mVH/1,000 ppm chloridesand/or more than 1,000

The present invention also provides a drilling line component and adrill stem comprising the above material.

A further aspect of the present invention is represented by a processfor making a material suitable for equipment in oilfield technology andhaving a relative magnetic permeability of less than 1.0048 μr, a yieldstrength (R_(p0.2)) of higher than 710 N/mm², a notched impact strengthof higher than 60 J, a fatigue strength under reversed stresses of atleast ±310 N/mm² at N=10⁷ load reversal and a fracture appearancetransition temperature (FATT) of below −28° C. The process comprises hotforming a material which consists essentially of, in percent by weight,≦0.03 C; ≦0.89 Si; 0.51 to 4.49 Mn; 25.1 to 38.9 Cr; 2.1 to 5.9 Mo; 22.9to 38.9 Ni; 0.51 to 1.49 Cu; and 0.17 to 0.29 N, with the balance ironand contaminants due to manufacture, in a condition free of nitrideprecipitates and without precipitated associated phases and, after acooling, cold forming the material in a condition free of ferrites.

In one aspect, the material contains any of the elements in thefollowing weight percentages: C≦0.02, e.g., 0.01 to 0.02; Si≦0.75, e.g.,0.20 to 0.70; Mn 1.1 to 2.9, e.g., 2.01 to 2.6; Cr26.1 to 27.9, e.g.,26.5 to 27.5;Mo 2.9 to 5.9, e.g., 3.2 to 3.8; Ni 27.9 to 32.5, e.g.,30.9 to 32.1; Cu 0.98 to 1.45, e.g., 1.0 to 1.4; and N 0.175 to 0.29,e.g., 0.18 to 0.22.

In another aspect, the process comprises hot forming the material atleast 3.6-fold and/or cold forming it with a degree of forming of lessthan 38%, e.g., 6 to 19%. In the case of cold forming, the formingtemperature may be from 100 to 590° C., e.g., from 360 to 490° C. Forexample, the material may be hot formed at least 3.6-fold and coldformed with a degree of forming of 6 to 19% at a temperature rangingfrom 360 to 490° C.

The advantages achieved by the invention lie in particular in thealloying technology effect of a balanced nitrogen concentration.Surprisingly, it was found that a particularly high output can beachieved in the manufacture of parts. Although there cannot be anynitride precipitates with a hot forming, the forming property of thematerial at a varying forging temperature is abruptly impaired atcontents of over 0.29 percent by weight nitrogen. In the narrowconcentration range of 0.17 to 0.29 percent by weight N a precipitationof associated phases can also be easily prevented if the other alloyingelements are present in the provided content ranges. Nitrogen, nickeland molybdenum thereby also synergistically produce an extremely highresistance to pitting.

At 0.03 percent by weight, the carbon content of the alloy has an upperlimit for corrosion chemistry reasons, with a further reduction thereofincreasing the corrosion resistance of the material, in particularpitting and stress corrosion cracking.

The silicon content in the material according to the invention shouldnot exceed 0.89 percent by weight for corrosion chemistry reasons and inparticular because of the low magnetic permeability.

The nitrogen solubility of the alloy and the austenite stabilization arepromoted by manganese. However, to prevent pitting, the manganesecontents must have an upper limit of 4.49 percent by weight with nickelbeing added to the alloy instead. A minimum content of 0.51 percent byweight manganese is necessary for an effective sulfur binding.

One of the particularly important alloying elements with regard tocorrosion resistance is chromium, because chromium is the basis forforming a passive layer on the surface of the parts. Contents of atleast 25.1 percent by weight Cr are necessary in synergistic effect withthe other alloying elements, in particular Mo and N, in order to largelyprevent a possible piercing of this layer in places. With contentshigher than 38.9 percent by weight the danger of a precipitation ofintermetallic phases increases.

Although the alloying element molybdenum is extremely important for aresistance of the material to crevice and pitting corrosion, the contentshould not exceed 5.9 percent by weight, because then there is a suddenincreased tendency to form associated phases. Contents lower than 2.1percent by weight impair the corrosion behavior of the materialdisproportionally.

The alloying element nickel is important in the provided concentrationsfor stabilizing the cubic face-centered atomic lattice, thus for lowpermeability, and interacting with chromium and molybdenum it iseffective for avoiding pitting corrosion. Up to 38.9 percent by weight,the toughness, the FATT and the fatigue strength under reversed stressesare advantageously increased. If it falls below 22.9 percent by weight,the stabilizing effect regarding corrosion, in particular stresscorrosion cracking, is reduced to an increasing extent inchloride-containing media and with respect to the magnetic values incold working; thus there is an increased tendency to form zones withstrain-induced martensite.

A copper content within the limits of the alloy is also provided toincrease corrosion resistance, even though the effect of this elementhas occasionally been questioned.

As mentioned earlier, the nitrogen content is synergistically adapted tothe remainder of the alloy composition. This content of 0.17 to 0.29percent by weight has the further advantage that a block can be left tosolidify under atmospheric pressure without gas bubbles being formedtherein by exceeding the solubility limit during solidification.

The magnetic, the mechanical and in particular the corrosion resistancevalues of the material can be set at a particularly high level, if itconsists essentially of the elements in percent by weight:

C = less than/equal to 0.02, preferably 0.005 to 0.02 Si = lessthan/equal to 0.75, preferably 0.20 to 0.70 Mn = 1.1 to 2.9., preferably2.01 to 2.6 Cr = 26.1 to 27.9, preferably 26.5 to 27.5 Mo = 2.9 to 5.9,preferably 3.2 to 3.8 Ni = 27.9 to 32.5, preferably 30.9 to 32.1 Cu =0.98 to 1.45, preferably 1.0 to 1.4 N = 0.175 to 0.29, preferably 0.18to 0.22 Fe and contaminants due to manufacture = balance.

High mechanical property values at a relative magnetic permeability of1.004 and below are achieved when the material is hot formed at least3.6-fold in a condition free of precipitates and is cold formed at atemperature of 100 to 590° C., preferably 360 to 490° C., with a degreeof forming of less than 38%, preferably 6 to 19%. According to theinvention the material features a pitting corrosion potential in aneutral solution at room temperature of more than 1,100 mVH/1,000 ppmchlorides and/or 1,000 mVH/80,000 ppm chlorides.

DESCRIPTION OF THE INVENTION

The invention is explained in more detail using examples.

Table 1 shows the chemical composition of the alloys according to theinvention and the comparison materials. The characteristic values forhot forming and cold forming the forged pieces can also be taken fromthis table.

The magnetic and the mechanical characteristic values of these materialscan be taken from Table 2.

Table 1 lists the comparison alloys with the sample identifiers 1through 5, and the alloys composed according to the invention with thesample identifiers A through E. The test results of the materials can betaken from Table 2. These results will be discussed briefly below.

The alloys 1 through 3 have low nitrogen contents, and therefore show nodesired hardening during a cold forming, as revealed by the R_(P0.2)values, and low numerical values of ±270, 210 and 290 N/mm² were alsoascertained for the fatigue strength under reversed stresses (not givenin the table).

In corrosion chemistry terms neither the SCC nor the CPT values areadequate, which can be attributed in particular to the respective low Mocontents and, in the case of material 2, to a low Cr content.

The alloys 4 and 5 have a not sufficiently high and an excessivenitrogen concentration, which leads to higher yield point values andalso increases the value for the fatigue strength under reversed bendingstresses (±308, 340 N/mm²). Due to a low Cr content, there is adisadvantageous DUAL microstructure (etching on the grain boundaries) inmaterial 4, and it should be further noted that, despite adequate Moconcentrations due to the lower Cr contents, material 5 does not meetthe requirements for corrosion-resistance, either. The results foralloys A through E show that the nitrogen contents lead to a desiredhardening by a cold forming, and the respective concentrations ofnitrogen, nickel and molybdenum synergistically give rise to a highcorrosion resistance of the material in chloride-containing media, inparticular a high resistance to pitting.

TABLE 1 1. Step/Hot Forming 2. Step Chemical Composition Degree ofForming Forming Forming Sample C Si Mn Cr Ni Mo Cu N Forming (-fold)Temp. [° C.] Cooling (%) Temp. [° C.] 1 0.02 0.31 1.92 27.20 30.66 0.300.60 0.02 4.5 1050/980 air 15 450 2 0.05 0.40 1.30 17.52 10.20 0.05 0.05n.d. 5.0 1070/910 water n.d. n.d. 3 0.025 0.41 2.51 25.28 28.07 0.35n.d. 0.08 5.2 1050/900 air 18 460 A 0.03 0.35 1.81 26.60 28.52 3.31 1.240.18 5.0 min. 850 water 15 480 B 0.025 0.28 2.25 27.44 34.58 3.78 1.300.21 5.8 min. 850 water 20 470 C 0.02 0.30 1.10 27.28 31.20 5.12 1.050.20 5.5 min. 850 water 18 470 D 0.025 0.28 1.60 30.56 35.38 2.20 0.700.28 5.2 min. 850 water 15 450 E 0.02 0.30 2.61 27.10 29.32 2.71 0.620.29 5.0 min. 850 water 20 480 4 0.01 0.6 1.7 17.30 13.20 2.7 0.01 0.165.0 1080/950 air 8 350 5 0.02 1.4 0.8 23.50 15.36 1.4 0.01 0.30 4.8 n.d.n.d. n.d. n.d. A, B, C, D, E = materials according to the invention 1 to5 = comparison materials

TABLE 2 Toughness Rel. Magn. (ISO-V) Oxalic Pitting PermeabilityR_(P0.2) Rm 20° C. FATT Acid Test SCC CPT Sample [μr] [N/mm²] [N/mm²][Joule] [° C.] ASTM-A262 45% MgCl₂ 22% NaCl 1 1.003 470 780 150 −45 STEP200 MPa/min. 720^(h) max. 5° C. 2 1.002 430 750 170 −50 STEP 100MPa/min. 8^(h ) max. 5° C. 3 1.003 560 790 160 −50 STEP 150 MPa/min.720^(h) max. 5° C. A 1.002 930 1050 140 −45 STEP 450 MPa/min. 720^(h)55° C. B 1.003 1010 1110 120 −45 STEP 550 MPa/min. 720^(h) 60° C. C1.003 940 1040 107 −40 STEP 650 MPa/min. 720^(h) 85° C. D 1.003 980 109099 −35 STEP 600 MPa/min. 720^(h) 65° C. E 1.002 1000 1150 130 −45 STEP450 MPa/min. 710^(h) 65° C. 4 1.005 670 820 130 −40 DUAL 100 MPa/min.720^(h) 15° C. 5 1.001 810 910 120 −45 STEP 150 MPa/min. 720^(h) 35° C.A, B, C, D, E = materials according to the invention 1 to 5 = comparisonmaterials

What is claimed is:
 1. A material suitable for equipment in oilfieldtechnology, consisting essentially of, in percent by weight: Carbon (C)≦0.03 Silicon (Si) ≦0.89 Manganese (Mn) 0.51 to 4.49 Chromium (Cr) 25.1to 38.9 Molybdenum (Mo) 2.1 to 5.9 Nickel (Ni) 22.9 to 38.9 Copper (Cu)0.51 to 1.49 Nitrogen (N) 0.17 to 0.29

with the balance iron and contaminants due to manufacture, whichmaterial is hot formed in a condition free of nitride precipitates andwithout precipitated associated phases and, after a cooling, cold formedin a condition free of ferrites, and having a relative magneticpermeability of less than 1.0048 μr, a yield strength (R_(p0.2)) ofhigher than 710 N/mm², a notched impact strength of higher than 60 J, afatigue strength under reversed stresses of at least ±310 N/mm² at N=10⁷load reversal, and a fracture appearance transition temperature (FATT)of below −28° C.
 2. The material of claim 1, wherein the C content is≦0.02 percent by weight.
 3. The material of claim 1, wherein the Sicontent is ≦0.75 percent by weight.
 4. The material of claim 1, whereinthe Mn content is 1.1 to 2.9 percent by weight.
 5. The material of claim1, wherein the Cr content is 26.1 to 27.9 percent by weight.
 6. Thematerial of claim 1, wherein the Mo content is 2.9 to 5.9 percent byweight.
 7. The material of claim 1, wherein the Ni content is 27.9 to32.5 percent by weight.
 8. The material of claim 1, wherein the Cucontent is 0.98 to 1.45 percent by weight.
 9. The material of claim 1,wherein the N content is 0.175 to 0.29 percent by weight.
 10. Thematerial of claim 2, wherein the C content is 0.01 to 0.02 percent byweight.
 11. The material of claim 3, wherein the Si content is 0.20 to0.70 percent by weight.
 12. The material of claim 4, wherein the Mncontent is 2.01 to 2.6 percent by weight.
 13. The material of claim 5,wherein the Cr content is 26.5 to 27.5 percent by weight.
 14. Thematerial of claim 6, wherein the Mo content is 3.2 to 3.8 percent byweight.
 15. The material of claim 7, wherein the Ni content is 30.9 to32.1 percent by weight.
 16. The material of claim 8, wherein the Cucontent is 1.0 to 1.4 percent by weight.
 17. The material of claim 1,wherein the N content is 0.18 to 0.22 percent by weight.
 18. Thematerial of claim 1, containing, in percent by weight: C ≦0.02 Si ≦0.75Mn 1.1 to 2.9 Cr 26.1 to 27.9 Mo 2.9 to 5.9 Ni 27.9 to 32.5 Cu 0.98 to1.45 N 0.175 to 0.29.


19. The material of claim 18, containing, in percent by weight: C 0.01to 0.02 Si 0.20 to 0.70 Mn 2.01 to 2.6  Cr 26.5 to 27.5 Mo 3.2 to 3.8 Ni30.9 to 32.1 Cu 1.0 to 1.4 N  0.18 to 0.22.


20. The material of claim 1, wherein the material is hot formed at least3.6-fold.
 21. The material of claim 20, wherein the material is coldformed with a degree of forming of less than 38%.
 22. The material ofclaim 21, wherein the degree of forming is 6 to 19%.
 23. The material ofclaim 21, wherein the material is cold formed at a temperature rangingfrom 100 to 590° C.
 24. The material of claim 22, wherein the materialis cold formed at a temperature ranging from 360 to 490° C.
 25. Thematerial of claim 19, wherein the material is hot formed at least3.6-fold and is cold formed with a degree of forming of 6 to 19% at atemperature ranging from 360 to 490° C.
 26. The material of claim 1,wherein the material has a pitting potential in a neutral solution atroom temperature of at least one of more than 1,100 mVH/1,000 ppmchlorides and more than 1,000 mVH/80,000 ppm chlorides.
 27. The materialof claim 25, wherein the material has a pitting potential in a neutralsolution at room temperature of at least one of more than 1,100mVH/1,000 ppm chlorides and more than 1,000 mVH/80,000 ppm chlorides.28. A drilling line component which comprises the material of claim 1.29. A drilling line component which comprises the material of claim 25.30. A drill stem which comprises the material of claim
 18. 31. A processfor making a material suitable for equipment in oilfield technology andhaving a relative magnetic permeability of less than 1.0048 μr, a yieldstrength (R_(p0.2)) of higher than 710 N/mm², a notched impact strengthof higher than 60 J, a fatigue strength under reversed stresses of atleast ±310 N/mm² at N=10⁷ load reversal and a fracture appearancetransition temperature (FATT) of below −28° C., said process comprisinghot forming a material consisting essentially of, in percent by weight:Carbon (C) ≦0.03 Silicon (Si) ≦0.89 Manganese (Mn) 0.51 to 4.49 Chromium(Cr) 25.1 to 38.9 Molybdenum (Mo) 2.1 to 5.9 Nickel (Ni) 22.9 to 38.9Copper (Cu) 0.51 to 1.49 Nitrogen (N) 0.17 to 0.29

with the balance iron and contaminants due to manufacture, in acondition free of nitride precipitates and without precipitatedassociated phases and, after a cooling, cold forming the material in acondition free of ferrites.
 32. The process of claim 31, wherein thematerial contains, in percent by weight: C ≦0.02 Si ≦0.75 Mn 1.1 to 2.9Cr 26.1 to 27.9 Mo 2.9 to 5.9 Ni 27.9 to 32.5 Cu 0.98 to 1.45 N  0.175to 0.29. 


33. The process of claim 32, wherein the material contains, in percentby weight: C 0.01 to 0.02 Si 0.20 to 0.70 Mn 2.01 to 2.6  Cr 26.5 to27.5 Mo 3.2 to 3.8 Ni 30.9 to 32.1 Cu 1.0 to 1.4 N  0.18 to 0.22.


34. The process of claim 32, wherein the material is hot formed at least3.6-fold.
 35. The process of claim 34, wherein the material is coldformed with a degree of forming of less than 38%.
 36. The process ofclaim 35, wherein the degree of forming is 6 to 19%.
 37. The process ofclaim 35, wherein the material is cold formed at a temperature rangingfrom 100 to 590° C.
 38. The process of claim 36, wherein the material iscold formed at a temperature ranging from 360 to 490° C.
 39. The processof claim 33, wherein the material is hot formed at least 3.6-fold and iscold formed with a degree of forming of 6 to 19% at a temperatureranging from 360 to 490° C.
 40. The process of claim 32, wherein thematerial suitable for equipment in oilfield technology is a drill linecomponent.